There are a variety of orbital track-traveling carriage mechanisms for performing welding of pipe joints or other vertical cylindrical members such as steel pipe, piles or tanks.
In the application of utilizing a cylindrical pipe as a foundation pile for a structure such as an offshore drilling rig, the length of the steel pipe required will, of course, vary according to the depth of the water at the site location. In the instance of providing a foundation for a structure on land, the length of the pipe will vary according to the subsoil structural conditions. For the longer lengths of structural pipe, it is often convenient or necessary to reduce the diameter of the pipe as the pile is driven deeper into the ground. Or, it may be necessary to use different sized pilings for different support members of the same or closely adjacent structures. In such event, it is necessary to employ a number of different welding units, each adapted for a particular size of steel pipe. This difference between the various welding units requires a substantial increase in the logistical support for a welding operation in a remote area. For example, if there were three different sized pipes being used to fabricate pilings and a number of varying-sized welding machines required for the different sizes of pilings, it would be necessary to maintain an inventory of spare welding units and parts for welding units in substantially greater numbers than would be required if a standard welding unit were available.
A straight line application would be the welding of a horizontal seam on the side of a marine vessel.
An additional problem in the use of welding machines which are used for welding circumferential workpieces arises when there is a requirement for welding, for example, a horizontal seam on a vessel of large diameter or with flat surfaces. The conventional circumferential welder will not adapt to such use, requiring yet another type of welding machine to be maintained.